A method using etching gas such as HF (hydrogen fluoride) gas or the like has been proposed as a micro-structure manufacturing method for forming a structure by dry-etching a sacrificial layer provided to a silicon substrate (see, for example, JP-A-5-275401, JP-A-7-99326).
The methods described in the above publications relate to a general dry etching method for a sacrificial layer, and use mixture gas of HF gas and H2O (water) as etching gas. When H2O is included as such an etching gas, it has been hitherto known that H2O has an adverse effect on etching.
Therefore, as the dry-etching method for the sacrificial layer has been proposed a method of using mixture gas of anhydrous HF gas and methanol (MeOH, CH3OH) gas as etching gas without containing H2O (Japanese Patent No. 2951922).
With respect to a sacrificial layer etching treatment using mixture gas of anhydrous HF gas and methanol gas as etching gas, the etching is carried out according to the reactions represented by the following chemical formulas 1 to 4. Here, the sacrificial layer is SiO2 (silicon oxide).anhydrous HF (gas)←→HF (adsorbed)   (Chemical formula 1)M (gas)←→M (adsorbed)   (Chemical Formula 2)2HF+M→HF2−+MH+  (Chemical Formula 3)SiO2+2HF2−+2MH+→SiF4↑+2H2O↑+2M↑  (Chemical Formula 4)Here, in the chemical formulas 1 to 4, M represents methanol, HF (gas) and HF (adsorbed) represent HF under gas and HF adsorbed by the silicon substrate respectively, and M(gas) and M(adsorbed) represent methanol under gas and methanol adsorbed by the silicon substrate.
As shown in these chemical formulas 1 to 4, in the sacrificial layer etching treatment using the mixture gas of anhydrous HF gas and methanol gas, HF and methanol are adsorbed to the silicon substrate (see the chemical formulas 1 and 2), and HF and methanol adsorbed to the substrate induce the chemical reactions shown in the chemical formulas 3 and 4, whereby SiO2 as the sacrificial layer is etched.
However, as shown in the chemical formula 4, H2O occurs as a reaction product. H2O is adsorbed to the silicon substrate again, and reacts with HF gas to etch SiO2 as the sacrificial layer.
As described above, etching dispersion in the silicon substrate plane is induced by H2O as the reaction product generated by the etching of the sacrifice, so that it is difficult to manage the etching quality and the etching rate.
In order to solve the problem of the etching dispersion caused by the reaction product, Japanese Patent No. 2951922 has proposed a method of preventing occurrence of residual materials by improving the upper and lower film structures of the sacrificial layer. According to this method, even when etching dispersion occurs, an etching stop layer is formed to regulate the etching region.
However, the method disclosed in the above publication needs a complicated structure, and thus increases the cost.